The invention relates to a field plate trench transistor and a method for producing it.
FIG. 1 illustrates an extract from a conventional field plate trench transistor to which the invention relates, particularly in cross-sectional illustration:
A field plate trench transistor (also referred to hereinafter as a trench transistor) 1 has a semiconductor body 2, in which the trench structure 3 and an electrode structure 4 embedded in the trench structure are provided. A cell array region (illustrated in the Figure) and an edge region (not illustrated in the Figure) are provided within the semiconductor body 2. That part of the semiconductor body 2 which is situated between the trenches of the trench structure 3 is also referred to as a “mesa structure”. The electrode structure 4 is electrically insulated from the semiconductor body 2 by means of an insulation structure 5 and has a gate electrode structure 6 and a field electrode structure 7 arranged below the gate electrode structure and electrically insulated from the latter. The semiconductor body 2 is subdivided into a body region 8, a drift region 9 and a drain region 10. Source regions 11 are formed in the body region 8. The body region 8 is electrically short-circuited with the source regions 11 via a source metallization 12. The drain region 10 is contact-connected by a drain metallization 13. The potential of the gate electrode structure 6 is at gate potential and the potential of the field electrode structure 7 is at source potential. The gate electrode structure 6 is electrically insulated from the source metallization 12 by means of an insulation structure 14.
What is disadvantageous about the trench transistor 1 described above is that in the off-state case, that region of the insulation structure 5 which is situated in the bottom of the trench structure 3 has to withstand virtually the full reverse voltage, which means that the thickness of the insulation structure 5 is not permitted to fall below a specific minimum value. This in turn has the consequence that limits are imposed on the degree of miniaturization of the trench structure 3 with performance parameters remaining the same.
In order to solve this problem, it is known to set the potential of the field electrode structure 7 in the off-state case to a potential lying between source potential and drain potential.
For these and other reasons, there is a need for the present invention.